The invention relates to a medium voltage circuit breaker with reduced operating energy having an elongated sealed enclosure filled with high dielectric strength gas, a pair of arcing contacts, one arcing contact being longitudinally slidable and adapted to occupy an open position in which the arcing contacts are separated and a closed position in which the arcing contacts are in abutment. The circuit breaker also includes a pair of main contacts, one main contract being movable, an operating mechanism requiring an operating energy substantially corresponding to that required to move the movable main contact and the movable arcing contact which are coupled to the mechanism. The mechanism is arranged to close the arcing contacts before the main contacts and to open the main contacts before the arcing contacts, and includes an arcing contact pressure spring, whose force corresponds to the electrodynamic repulsion forces of the arcing contacts generated by the current flow.
A circuit breaker of the kind referred to above enables the main contacts to be open and closed without an arc, the current being shunted by the arcing contacts. Shunting of the current by the arcing contacts can be performed only if the latter are correctly closed, and it is therefore indispensable to prevent opening due to the effect of the electrodynamic repulsion forces. The force of the arcing contact pressure spring must be able to overcome these repulsion forces, and it is dimensioned accordingly. This spring is compressed at each operation by the operation mechanism which supplies it with a corresponding energy.
In a state-of-the-art circuit breaker (U.S. Pat. No. 4,309,581) with gas self-blast, this energy is recovered when the circuit breaker opens and is used to move the arc blowout gas compression piston.
The development of new breaking techniques, i.e. breaking by auto-expansion and/or rotating arc and vacuum breaking noting (U.S. Pat. Nos. 4,737,607 and 5,155,315) has enabled the gas-blast pistons to be suppressed, and the energy stored in the contact pressure spring is recovered by the mechanism, equipped with damper or energy dissipating systems.
The present invention is based on the observation that the contact pressure at the level of the arcing contacts is only useful during a short period when the current is branched off through the arcing contacts. So long as or as soon as the main contacts are closed, the current flows through these main contacts and the arcing contacts are not subjected to any repulsion effect. The arm of the present invention is to reduce as far as possible the energy required for operation of the circuit breaker and notably the energy for compression of the arcing contact compression spring. It also aims to reduce the contact pressure when the circuit breaker is closed, thus reducing the stresses exerted on the enclosure, generally made of resin, and the risks of creep.